Fluid-mold casting slag



y 1959 J. E. RQBERTS 3,444,010

FLUID-MOLD CASTING SLAG Filed Oct. 5, 1966 INVENTOR JAMES EARL ROBERTSATTORNEY 3,444,010 FLUID-MOLD CASTING SLAG James E. Roberts, Huntington,W. Va., assignor to The International Nickel Company, Inc., New York,N.Y., a corporation of Delaware Filed Oct. 3, 1966, Ser. No. 583,911Int. Cl. C23c 1/12 U.S. (Tl. 14822 Claims The present invention isdirected to an improvement in the fluid-mold casting process to produceingot castings made of nickel and nickel-containing alloys havingimproved surface and improved metallurgical quality and to a specialcasting slag composition for use in such a process.

The fluid-mold casting process has now been available to the art for anumber of years and has been employed successfully in connection withthe production of ingot castings made of a number of different metals.In accordance with the process, a quantity of molten slag is placed atthe bottom of an ingot mold and molten metal conditioned for theproduction of an ingot is teemed into the mold through the slag. Duringteeming, the slag advances upward on the surface of the metal and formsa thin coating on the ingot mold surface. The coating remains during thecasting process and separates the ingot from the ingot mold. Whenconditions in respect of metal and slag temperature, melting point andcomposition of the metal and the slag are compatible, an ingot isproduced having a greatly improved surface as compared to that obtainedwhen no casting Slag is employed. The initial work conducted inaccordance with the fluid-mold casting process involved the use ofsilicate type slags. These slags operated successfully in conjunctionwith the casting of metals such as mild steel and stainless steel.However, when it was attempted to use the silicate type slags withnickel and nickel-base alloys, it was found that numerous difficultieswere encountered. Thus, with many alloys, an intolerable pick-up ofsilicon in the ingot resulting from interaction between the molten metaland molten slag was encountered, yielding ingots which did not meetchemical specifications. In addition, defects were encountered in thesurface of many ingots which have been classified as notch defect, aperipheral indentation about the ingot toward the toe portion and asshotted-surface defect, which apparently involves emulsification of slagand metal and is usually most evident toward the top of the ingot. Thesedefects required extensive and expensive overhaul of the ingots beforefurther mill processing could be successfully undertaken. The result hasbeen that the advantages contemplated through the use of the fluid-moldslag casting process, namely, improved ingot yield and better ingotsurface, were not obtained in many instances. A further development inrelation to slag chemistry involved the deletion of silica as a slagconstituent and the use of a titaniacalcium oxide-alumina type slag toprovide an improved fluid-mold casting composition for use withnickel-containing alloys, particularly of the age hardening types.Further experience with this slag material has demonstrated that evenfurther improvement was necessary. For example, it was found that in thefluid-mold casting of nickel ingots intended for the production ofwrought nickel products for electronic uses, an intolerable pick-up oftitanium from the slag was encountered. This resulted in ingots whichwere chemically out of definition and which were not acceptable.Furthermore, it was found that while in many instances highlysatisfactory ingot surfaces were obtained in the production of nickeland nickel alloy ingots with the improved slag, that in other instancesunsatisfactory ingot surfaces, e.g., shotted surface, were stillobtained.

3,444,010 Patented May 13, 1969 I have now discovered an improvedcasting slag com position and process for fluid-mold casting of nickel,nickel-base and nickel containing alloys which provides improved ingotsurfaces and greater recovery of metal from the ingot into hot rolledproducts.

It is an object of the present invention to provide an improvedfluid-mold casting slag particularly useful for the production of ingotsmade of nickel and nickel-containing alloys.

Another object of the invention is to provide a fluidmold castingprocess applicable to nickel and nickel-containing alloys which providesimproved ingot surface and improved metal yield upon hot rolling of theingots, as well as improved metallurgical quality.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawing in which:

FIGURE 1 is a reproduction of a photograph depicting the surface of ainch square by 90 inch long nickel ingot produced in accordance with theconcepts of the present invention.

FIGURE 2 is a reproduction of a photograph depicting the surface of a 20inch square by 90 inch long nickelchromium-iron alloy ingot produced inaccordance with the invention, and

FIGURE 3 is a reproduction of a photograph of a hot rolled billetproduced from an age hardenable nickelchromium alloy ingot cast inaccordance with the invention which was hot rolled without any surfaceoverhauling.

Generally speaking, the present invention is directed to a casting slagcomposition consisting essentially of, by weight, about 2.0% to about40% alumina, about to about 50% calcium oxide, with the alumina contentnot exceeding the calcium oxide content by more than 5 weight percent,about 5% to about 20% magnesium oxide, about 3% to about 10% sodiumoxide, and about 10% to about of an alkaline earth fluoride ingredientfrom the group consisting of cryolite (Na AlF potassium aluminumfluoride (K AlF and fluorspar (CaF Advantageously, the casting slagcomposition contains about to about 50% calcium oxide, about 25% toabout alumina, about 5% to about 15% magnesia, about 10% to about 30% ofan alkaline earth fluoride from the group consisting of cryolite,potassium aluminum fluoride, calcium fluoride and about 3% to about 10%sodium oxide. A preferred slag composition contains about 35% to about40% calcium oxide, about 25% to about 40% alumina, about 5% to about 8%magnesia, about 10% to about 20% cryolite, about 5% to about 10%fluorspar and about 3% to about 6% sodium oxide. The slags produced inaccordance with the invention have a flow point on heating in the temperature range of about 2300 F. to about 2450 F. The special slagcompositions are essentially devoid of silica and titania, although, insome instances, for example, those in which minor pick-up of silicon ispermissible, up to about 3% silica may be present. Titania should notexceed about 0.5%, by weight, e.g., 0.1% or 0.2%. Metal oxides such asmanganese oxide, chromium oxide, nickel oxide and copper oxide arepreferably absent but may be in some cases present in amounts up toabout 1% each. Impurities harmful to nickel and nickel alloys, includingarsenic, lead, tin, zinc, sulfur, etc., should be absent from the slag.For purposes of controlling the flow point on heating the slag to be inthe advantageous neighborhood of 2300 F. to about 2450 F. in the case ofnickel and nickel-containing alloys, including nickel-chromium,nickel-chrom'ium-iron, nickel-copper alloys, cupronickel alloys, etc.,the ingredients for forming the slag are carefully proportioned. Thebulk of the slag composition comprises calcium oxide and alumina withthe alumina being present in amounts not exceeding the calcium oxide bymore than weight percent. Magnesia and sodium oxide in the controlledamounts specified hereinbefore assist in controlling the melting point.Magnesia is employed in amounts not exceeding 20% and preferably notexceeding about since greater amounts undesirably raise the slag meltingpoint. The fluoride ingredients, namely, cryolite, potassium aluminumfluoride and fluorspar, are employed in the amounts described forpurposes of pared in a submerged electrode furnace and was heated toabout 3100 F. inch by 20 inch square ingot molds were set up on copperstools. About 250 pounds of the molten casting slag was poured into thebottom of the first ingot mold. This was sufficient to extend upwardswithin the ingot mold and cover about 3 inches vertically at the bottomof the mold. Nickel from the induction furnace heat was teemed from abottom pour ladle at a temperature of about 2870 F. into the ingot moldat a steady rate through the slag pool to completely fill the ingot withfurther controlling fluidity and melting point of the slag. 10 metal andflush the excess casting slag from the top of In compounding the slag,it is important that the dry inthe mold. The remaining ingot molds werethen filled in gredients be thoroughly blended prior to melting sincethe same manner. Metal from the ingots met the rigid it is otherwisefound impractical to secure a uniform slag chemical specification forthis grade of material. The recomposition in the melting procedure.Melting advansulting ingots were inspected and found to have anexceltageously is conducted in a submerged electrode furnace. lentsurface which permitted them to be hot rolled with- A number ofsatisfactory slag compositions are set forth out any surfaceoverhauling. The surface of one of the in the following Table I: ingotsis depicted in the accompanying FIGURE 1.

TABLE I 0210, A1203, MgO, CaFz, Na AlFn, K AlFe, NagO, Flow point onSlag No percent percent percent percent percent percent percent heating,F.

The special casting slag composition is particularly advantageous forthe production of ingots in commercial wrought nickel containing 99% andmore of nickel,

nickel-copper alloys containing 50% or more of nickel, 30

cupronickel alloys containing nickel in amounts as low as about 29% andthe balance essentially copper, and nickel-chromiunr-iron alloyscontaining 30% or more of nickel, up to 50% of iron and up to 30% ofchromium.

The alloys may also contain other usual alloying ingredients such as upto about 10% molybdenum, up to about 10% columbium, up to about 30%cobalt, up to about 5% tungsten, up to about 5% manganese, up to about3% silicon, up to about 0.5% carbon, up to about 2% vanadium, up toabout 6% aluminum, up to about 40 It was found that the use of thespecial casting slag in accordance with the foregoing example eliminatedthe ingot cracking problem which has been encountered duringsolidification of nickel ingots heretofore. Such cracks rupture duringhot working with major losses of metal. Elimination of the ingotcracking and the ingot overhauling in this electronic grade of nickelprovides a yield increase at the hot rolling stage on the order of 6% to8% by Weight. The fluid-mold cast material was not only hot rolled fromthe ingot stage without overhaul of the ingot surface but it was foundthat when the material was worked down into strip form blistering was70% less than on strip produced from non-flux cast ingots.

Example II An ingot of a nickel-chomium-iron alloy containing about 32%nickel, about 0.04% carbon, about 0.75% manganese, about 0.35% silicon,about 0.3% copper, about 20.5% chromium, and the balance essentiallyiron, was produced by the fluid-mold process employing a fluidmoldcasting slag having the composition set forth in TAB LE II PercentPercent Percent Percent Percent Percent Percent Percent Percent Percent09 Ni 0 Mn Fe Si C Cr Al Ti th In order to give those skilled in the arta better understanding of the invention, the following illustrativeexamples are given:

Example I A melt weighing about 9880 pounds made of a commercially purenickel alloy containing about 99.5% nickel, about 0.09% carbon, not morethan 0.3% manganese, not more than about 0.1% iron, not more than about0.1% silicon, not more than about 0.1% copper, and not more than about0.003% titanium was prepared for easting in an induction furnace. Acasting slag melt made from a charge of blended dry ingredientscontaining about 37% calcium oxide, about 37% alumina, about 6%magnesia, about 5% fluorspar, about 10% cryolite and about 5% sodiumoxide added as sodium carbonate was pre- Example I. When the ingot wasstripped from the mold, it was found to have a high quality surface freefrom the shotting defect. The appearance of the ingot is depicted in theaccompanying FIGURE 2. The highly satisfactory result achieved with thismaterial contrasts With the results obtained in fluid-mold casting thealloy using both the silicate type slag and the titania-lime-ahuninaslag of the prior art. Each of the prior art casting slags resulted in ashotted surface with this alloy. Thus, with the silicate type slag aboutof ingots produced from this alloy required milling and about 60% ofingots produced in this alloy using the titania-lime-alumina slagrequired milling. However, the ingots produced with the new fluid-moldcasting composition described herein could be hot rolled 7 without ingotoverhauling thereby enabling a yield increase at the hot rolled stage onthe order of 3% to by Weight.

Example III Ingots made of an age hardenable nickel-chromium alloycontaining about 7% iron, about 16% chromium, about 3% titanium, about0.04% carbon, about 0.15% silicon, and the balance essentially nickel,were produced by the fluid-mold casting process employing a slag havingthe composition set forth in Example I. The ingots were 18 inches squareand 48 inches long. Ingots stripped from the mold demonstrated anexcellent surface which permitted hot rolling to bloom without ingotoverhaul. The surface of a hot rolled shape having a 10 inch by inchsection produced from the 18 inch square ingot of this alloy withoutingot overhaul is depicted in the accompanying FIGURE 3. It was foundthat with this particular alloy the prior fluid-mold casting slags didnot produce results any better than those achieved with no slag at all.The ability to produce the high quality ingot surface on this alloyusing the special fluid-mold casting slag of the present inventionenables a yield increase at the hot rolled stage on the order of about10% by weight as compared to prior practice.

The special fluid-mold casting slag compositions provided in accordancewith the invention must be carefully controlled to secure the desiredresults. In particular, the alumina content should not exceed the limecontent by more than 5 weight percent while maintaining other slagingredients in the ranges set forth hereinbefore or it becomesimpractical to obtain the required melting point even with the use offluoride ingredients. For example, a slag containing 5 moles of C210 and3 moles of A1 0 with no other ingredients representing a weight contentof 52.5% A1 0 has a flow point on heating which is far in excess of2450" F. and remains too sluggish and refractory to produce good nickelalloy ingot surfaces in slag casting even when diluted with a fluorideingredient such as fiuorspar.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

1. A fluid-mold casting slag composition consisting essentially of, byweight, about 20% to 40% alumina, about to 50% calcium oxide, with thealumina content not exceeding the calcium oxide content by more than 5weight percent, about 5% to about 20% magnesium oxide, about 3% to about10% sodium oxide, and about 10% to about of an alkaline earth fluoride.

2. A casting slag in accordance with claim 1 containing about to aboutcalcium oxide, about 25 to about 40% alumina, about 5% to about 15%magnesia, about 3% to about 10% sodium oxide and about 10% to about30%.of an alkaline earth fluoride.

3. A casting slag in accordance with claim 1 containing about 35% toabout 40% calcium oxide, about 25 to about 40% alumina, about 5% toabout 8% magnesia, about 3% to about 6% sodium oxide, about 10% to about20% cryolite and about 5% to about 10% fluorspar.

4. A casting slag in accordance with claim 1 containing about 35% toabout 43% calcium oxide, about 27% to about 37% alumina, about 6% toabout 10% magnesia, about 5% sodium oxide and about 15 to about 19% of afluoride ingredient from the group consisting of fluorspar, cryolite andpotassium aluminum fluoride.

5. A casting slag in accordance with claim 1 containing about 37%calcium oxide, about 37% alumina, about 6% magnesia, about 5% sodiumoxide, about 5% calcium fluoride and about 10% cryolite.

References Cited UNITED STATES PATENTS 2,493,394 1/1950 Dunn et a1.164133 2,631,344 3/1953 Kennedy l64l33 3,214,806 11/1965 Fox et al.164133 3,224,887 12/1965 Fox et a]. 106--38.27

L. DEWAYNE RUTLEDGE, Primary Examiner. W. W. STALLARD, AssistantExaminer.

US. Cl. X.R.

1. A FLUID-MOLD CASTING SLAG COMPOSITION CONSISTING ESSENTIALLY OF, BYWEIGHT, ABOUT 20% TO 40% ALUMINA, ABOUT 25% TO 50% CALCIUM OXIDE, WITHTHE ALUMINA CONTENT NOT EXCEEDING THE CALCIUM OXIDE CONTENT BY MORE THAN5 WEIGHT PERCENT, ABOUT 5% TO ABOUT 20% MAGNESIUM OXIDE, ABOUT 3% TOABOUT 10% SODIUM OXIDE, AND ABOUT 10% TO ABOUT 30% OF AN ALKALINE EARTHFLUORIDE.